Method and apparatus for establishing peer-to-peer communication

ABSTRACT

A method and apparatus for establishing peer-to-peer communication and performing forwarding under the control of a cellular network are described. A seeking wireless transmit/receive unit (WTRU) may receive a timing signal from at least one discoverable WTRU controlled by a base station. The seeking WTRU may estimate the quality of a radio link (i.e., path loss) between the seeking WTRU and the discoverable WTRU, and determine, (e.g., based on a threshold established by the base station), whether or not to report the estimated radio link quality to a base station that controls the discoverable WTRU. The power of the timing signal may be ramped up in predetermined steps such that the transmission power at any given time is known and may be used by the seeking WTRU for estimating the radio link quality. The timing signal may include at least one of a primary preamble or a secondary preamble.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application Nos.61/410,146 filed Nov. 4, 2010, 61/448,941 filed Mar. 3, 2011, and61/494,721 filed Jun. 8, 2011, the contents of which are herebyincorporated by reference herein.

BACKGROUND

In a cellular network, several states and corresponding behaviors may bedefined for a plurality of wireless transmit/receive units (WTRUs) and anetwork including at least one base station (BS). In a disconnectedmode, a WTRU may be aware of its rough geographical area and may notifythe network of any change in the geographical area so that the networkknows where the WTRU is to be paged. The WTRU may monitor for pagingduring the disconnected mode. In order to know its geographical area,the WTRU may need to recognize at least one cell in its immediate area,or search for other cells to obtain sufficient information to recognizeits area.

When necessary, the WTRU may switch to a connected mode from thedisconnected mode. In order to do so, the WTRU may identify thestrongest cell in the area and receive the necessary information todetermine its access mode. The WTRU may use a common (contention based)channel to access a cell. After some interactions, the WTRU mayestablish connections (service flows) as necessary in the connectionmode. Once connections are established, the WTRU may have resourcesassigned to it and may request additional bandwidth as necessary.

It may be desirable for a WTRU to collaborate in the relaying of datato/from the network, or to communicate data locally without data flowsto/from a base station. Various procedures are needed to support suchcollaboration by enabling the WTRU, possibly assisted by the network, toidentify and maintain an association with at least one other WTRU.

SUMMARY

A method and apparatus for establishing peer-to-peer communication andforwarding under the control of a cellular network are described. Aseeking wireless transmit/receive unit (WTRU) may receive a timingsignal from at least one discoverable WTRU controlled by a base station.The seeking WTRU may estimate the quality of a radio link (i.e., pathloss) between the seeking WTRU and the discoverable WTRU, and determine,(e.g., based on a threshold established by the base station), whether ornot to report the estimated radio link quality to a base station thatcontrols the discoverable WTRU. The power of the timing signal may beramped up in predetermined steps such that the transmission power at anygiven time is known and may be used by the seeking WTRU for estimatingthe radio link quality. The timing signal may include at least one of aprimary preamble or a secondary preamble. Alternatively, after receivingthe timing signal, the seeking WTRU may send a handshake seeking signalto the at least one discoverable WTRU, which may respond by sendinganother timing signal and network access information.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A shows an example communications system in which one or moredisclosed embodiments may be implemented;

FIG. 1B shows an example wireless transmit/receive unit (WTRU) that maybe used within the communications system shown in FIG. 1A;

FIG. 1C shows an example radio access network and an example corenetwork that may be used within the communications system shown in FIG.1A;

FIG. 2 shows an example network including a seeking WTRU and adiscoverable WTRU configured to perform an access initializationprocedure;

FIGS. 3A and 3B are flow diagrams of procedures used to achievesufficient synchronization between a seeking WTRU and a discoverableWTRU;

FIG. 4 shows an example of placement of a timing signal (TS) in asuperframe;

FIG. 5 shows an example of transmission opportunities for sounding as anhandshake seeking signal (HSS) in a time division duplex (TDD) frame;

FIG. 6 shows an example of a plurality of superframes used by a basestation, two discoverable WTRUs and two seeking WTRUs;

FIG. 7 shows an example procedure implemented when a seeking WTRU and adiscoverable WTRU are under the control of a base station; and

FIG. 8 is a block diagram of an example base station used to perform theprocedure of FIG. 7.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. AWTRU may be a non-infrastructure node.

When referred to hereafter, the terminology “seeking WTRU” includes butis not limited to a WTRU attempting to discover and associate withpeers.

When referred to hereafter, the terminology “discoverable WTRU” includesbut is not limited to a WTRU that may be discovered by the seeking WTRU.

When referred to hereafter, the terminology “base station” includes butis not limited to a Node-B, a site controller, an access point (AP), orany other type of interfacing device capable of operating in a wirelessenvironment.

FIG. 1A shows an example communications system 100 in which one or moredisclosed embodiments may be implemented. The communications system 100may be a multiple access system that provides content, such as voice,data, video, messaging, broadcast, and the like, to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include WTRUs 102a, 102 b, 102 c, 102 d, a radio access network (RAN) 104, a core network106, a public switched telephone network (PSTN) 108, the Internet 110,and other networks 112, though it will be appreciated that the disclosedembodiments contemplate any number of WTRUs, base stations (BSs),networks, and/or network elements. Each of the WTRUs 102 a, 102 b, 102c, 102 d may be any type of device configured to operate and/orcommunicate in a wireless environment. By way of example, the WTRUs 102a, 102 b, 102 c, 102 d may be configured to transmit and/or receivewireless signals and may include user equipment (UE), a mobile station,a fixed or mobile subscriber unit, a pager, a cellular telephone, apersonal digital assistant (PDA), a smartphone, a laptop, a netbook, apersonal computer, a wireless sensor, consumer electronics, and thelike.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the other networks 112. By way of example, the base stations 114a, 114 b may be a base transceiver station (BTS), a Node-B, an evolvedNode-B (eNB), a Home Node-B (HNB), a Home eNB (HeNB), a site controller,an access point (AP), a wireless router, and the like. While the basestations 114 a, 114 b are each depicted as a single element, it will beappreciated that the base stations 114 a, 114 b may include any numberof interconnected base stations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, and the like. The base station 114 a and/or the base station 114b may be configured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple-output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link, (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, and thelike). The air interface 116 may be established using any suitable radioaccess technology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as universal mobiletelecommunications system (UMTS) terrestrial radio access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as high-speed packet access(HSPA) and/or evolved HSPA (HSPA+). HSPA may include high-speed downlink(DL) packet access (HSDPA) and/or high-speed uplink (UL) packet access(HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as evolved UTRA (E-UTRA),which may establish the air interface 116 using long term evolution(LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,worldwide interoperability for microwave access (WiMAX)), CDMA2000,CDMA2000 1X, CDMA2000 evolution-data optimized (EV-DO), Interim Standard2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856(IS-856), global system for mobile communications (GSM), enhanced datarates for GSM evolution (EDGE), GSM/EDGE RAN (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, HNB, HeNB,or AP, for example, and may utilize any suitable RAT for facilitatingwireless connectivity in a localized area, such as a place of business,a home, a vehicle, a campus, and the like. In one embodiment, the basestation 114 b and the WTRUs 102 c, 102 d may implement a radiotechnology such as IEEE 802.11 to establish a wireless local areanetwork (WLAN). In another embodiment, the base station 114 b and theWTRUs 102 c, 102 d may implement a radio technology such as IEEE 802.15to establish a wireless personal area network (WPAN). In yet anotherembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayutilize a cellular-based RAT, (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A,and the like), to establish a picocell or femtocell. As shown in FIG.1A, the base station 114 b may have a direct connection to the Internet110. Thus, the base station 114 b may not be required to access theInternet 110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over Internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, prepaid calling, Internet connectivity, video distribution,and the like, and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe Internet protocol (IP) in the TCP/IP suite. The networks 112 mayinclude wired or wireless communications networks owned and/or operatedby other service providers. For example, the networks 112 may includeanother core network connected to one or more RANs, which may employ thesame RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B shows an example WTRU 102 that may be used within thecommunications system 100 shown in FIG. 1A. As shown in FIG. 1B, theWTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element, (e.g., an antenna), 122, a speaker/microphone124, a keypad 126, a display/touchpad 128, a non-removable memory 130, aremovable memory 132, a power source 134, a global positioning system(GPS) chipset 136, and peripherals 138. It will be appreciated that theWTRU 102 may include any sub-combination of the foregoing elements whileremaining consistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), amicroprocessor, one or more microprocessors in association with a DSPcore, a controller, a microcontroller, an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA)circuit, an integrated circuit (IC), a state machine, and the like. Theprocessor 118 may perform signal coding, data processing, power control,input/output processing, and/or any other functionality that enables theWTRU 102 to operate in a wireless environment. The processor 118 may becoupled to the transceiver 120, which may be coupled to thetransmit/receive element 122. While FIG. 1B depicts the processor 118and the transceiver 120 as separate components, the processor 118 andthe transceiver 120 may be integrated together in an electronic packageor chip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. The transmit/receiveelement 122 may be configured to transmit and/or receive any combinationof wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122, (e.g., multipleantennas), for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),and the like), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station, (e.g., base stations 114 a, 114 b), and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. The WTRU 102 may acquire location informationby way of any suitable location-determination method while remainingconsistent with an embodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C shows an example RAN 104 and an example core network 106 thatmay be used within the communications system 100 shown in FIG. 1A. TheRAN 104 may be an access service network (ASN) that employs IEEE 802.16radio technology to communicate with the WTRUs 102 a, 102 b, 102 c overthe air interface 116.

As shown in FIG. 1C, the RAN 104 may include base stations 140 a, 140 b,140 c, and an ASN gateway 142, though it will be appreciated that theRAN 104 may include any number of base stations and ASN gateways whileremaining consistent with an embodiment. The base stations 140 a, 140 b,140 c may each be associated with a particular cell (not shown) in theRAN 104 and may each include one or more transceivers for communicatingwith the WTRUs 102 a, 102 b, 102 c over the air interface 116. In oneembodiment, the base stations 140 a, 140 b, 140 c may implement MIMOtechnology. Thus, the base station 140 a, for example, may use multipleantennas to transmit wireless signals to, and receive wireless signalsfrom, the WTRU 102 a. The base stations 140 a, 140 b, 140 c may alsoprovide mobility management functions, such as handoff triggering,tunnel establishment, radio resource management, traffic classification,quality of service (QoS) policy enforcement, and the like. The ASNgateway 142 may serve as a traffic aggregation point and may beresponsible for paging, caching of subscriber profiles, routing to thecore network 106, and the like.

The air interface 116 between the WTRUs 102 a, 102 b, 102 c and the RAN104 may implement the IEEE 802.16 specification. In addition, each ofthe WTRUs 102 a, 102 b, 102 c may establish a logical interface (notshown) with the core network 106. The logical interface between theWTRUs 102 a, 102 b, 102 c and the core network 106 may be used forauthentication, authorization, IP host configuration management, and/ormobility management.

The communication link between each of the base stations 140 a, 140 b,140 c may include protocols for facilitating WTRU handovers and thetransfer of data between base stations. The communication link betweenthe base stations 140 a, 140 b, 140 c and the ASN gateway 142 mayinclude protocols for facilitating mobility management based on mobilityevents associated with each of the WTRUs 102 a, 102 b, 102 c.

As shown in FIG. 1C, the RAN 104 may be connected to the core network106. The communication link between the RAN 104 and the core network 106may include protocols for facilitating data transfer and mobilitymanagement capabilities, for example. The core network 106 may include amobile IP home agent (MIP-HA) 144, an authentication, authorization,accounting (AAA) server 146, and a gateway 148. While each of theforegoing elements are depicted as part of the core network 106, it willbe appreciated that any one of these elements may be owned and/oroperated by an entity other than the core network operator.

The MIP-HA 144 may be responsible for IP address management, and mayenable the WTRUs 102 a, 102 b, 102 c to roam between different ASNsand/or different core networks. The MIP-HA 144 may provide the WTRUs 102a, 102 b, 102 c with access to packet-switched networks, such as theInternet 110, to facilitate communications between the WTRUs 102 a, 102b, 102 c and IP-enabled devices. The AAA server 146 may be responsiblefor user authentication and for supporting user services. The gateway148 may facilitate interworking with other networks. For example, thegateway 148 may provide the WTRUs 102 a, 102 b, 102 c with access tocircuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. In addition, the gateway 148 mayprovide the WTRUs 102 a, 102 b, 102 c with access to the networks 112,which may include other wired or wireless networks that are owned and/oroperated by other service providers.

Although not shown in FIG. 1C, it will be appreciated that the RAN 104may be connected to other ASNs and the core network 106 may be connectedto other core networks. The communication link between the RAN 104 theother ASNs may include protocols for coordinating the mobility of theWTRUs 102 a, 102 b, 102 c between the RAN 104 and the other ASNs. Thecommunication link between the core network 106 and the other corenetworks may include protocols for facilitating interworking betweenhome core networks and visited core networks.

Various non-traditional applications for cellular networks are beingconsidered that involve communications not initiated by humans and notstrictly hierarchical topologies, such as machine-to-machine (M2M)communications or machine type communications (MTC). The M2Mcommunications or MTC are defined as communications initiated by amachine to communicate with either other machines or humans. The methodsdescribed herein may be applicable to MTC communications, as well asother types of communications.

Network topologies which include WTRU-to-WTRU direct communications,(also referred to as peer-to-peer communications), may be used forcoverage extension, throughput improvement, and the like. These networktopologies may also significantly increase network robustness byproviding an alternative path for connectivity, by finding(“discovering”) nodes when necessary. However, the WTRUs may not bemobile at all, or have a very low mobility.

Changes to the traditional behavior of a WTRU with respect to the way itfinds and establishes a link with the network are necessary, includingthe functionality of node discovery, routing, association and bandwidthrequest, as appropriate. A WTRU, possibly assisted by the network, mayapply to identify and maintain an association with a set of other WTRUsto either assist in relaying of data to/from the network, or communicatedata locally without data flows to/from a base station. Clientcollaboration, relaying and WTRU-to-WTRU communication with or without anetwork may be implemented in any type of wireless communication systemsincluding, but not limited to, IEEE 802.16 and any amendments thereof,long term evolution (LTE), universal mobile telecommunication system(UMTS), and the like.

Examples of peer-to-peer connections for machine type communications forsome use cases are described herein. The node discovery and associationmay accommodate the following use cases, as an example: (1) M2Mcommunications, (2) network robustness, and (3) throughput enhancement.There may be many different use cases and the examples disclosed hereinmay be applicable to any other use cases.

An example of the M2M communications case may be smart gridapplications. It may be typified by low or no mobility, low sensitivityto latency and tight battery consumption requirements. For thisapplication, in a typical node discovery scenario, one WTRU that cannotdetect a base station in the area may attempt to discover and associatewith other WTRU to act as relays on its behalf. Due to low mobility, thenode discovery is a rare event.

An example of the network robustness case is a typical network thatneeds to recover from node failures, including failures of theinfrastructure nodes. Such networks may be used for public protectionand disaster recovery (PPDR), (also known as “first responders”), and inM2M applications (e.g., surveillance). In these networks, highermobility may be required. The higher mobility results in a higher nodediscovery event rate. As in the M2M communications case, some of thedevices may not have an access to the network, or network infrastructurenodes may not exist.

For the throughput enhancement case, both seeking WTRUs and discoverableWTRUs may communicate with the base station at some nominal data ratethat is sufficient for the required control signaling. They may need totransmit and receive data at a much higher data rate, either betweenthem or to and from the network.

Different use cases may require different node discovery and associationmechanisms. Examples are disclosed for a framework that may accommodateall use cases.

The following are example goals of the design that are independent ofthe use cases: minimize impact on current standards, in particularphysical layer; minimize interference created by signals (e.g., apreamble) necessary for the node discovery to preambles or other signalsof infrastructure nodes or other WTRUs, minimize battery consumption,minimize latency, expedite discovery and association, share the network(infrastructure nodes and spectrum) with “normal” users, control ofresources, improvement of system throughput by increasing reuse of radioresources, and the like.

An M2M communications case (as typified by Smart Grid) is describedherein. This case may be typified by a large number of devices that areat low or no mobility. Data transmission may be generally infrequent andmay tolerate relatively high latency. Data transmission may be eventdriven (e.g., power outage) and then requires tighter latency. Smartgrid devices may share the network with other types of devices. Due tothe characteristics above, network entry and re-entry may happeninfrequently. Because of the large number of M2M devices in the networkand the need to share it with other types of devices, interferencecreated by the signals that are transmitted in order to be discoveredmay need to be minimized.

The WTRU-WTRU node discovery process may be performed when the device ispowered up and the association established may be applicable withoutfurther updates due to the very low and no mobility. WTRUs associatedwith the network may be in a standby mode (i.e., “sleeping”) most of thetime to minimize battery consumption. Signals used for network accessmay cause as little interference as possible.

WTRU-WTRU interaction without infrastructure (public protection anddisaster recovery (PPDR) applications) is described herein. This casemay be typified by cellular mobility and by the absence of networkinfrastructure nodes. As communication is peer to peer, it may not befeasible to perform pairwise access for all pairs of mobiles in thenetwork. Therefore, access may be done just prior to sending data. As aresult, access may need to be quick. Battery consumption is importantbut perhaps not over the other goals. The WTRU-WTRU node discovery maybe performed during the transition to the connected mode prior to theoccurrence of peer-to-peer data communication, and in this sense may beconsidered event triggered.

WTRU-WTRU interaction under the control of a base station, (throughputenhancement (TE) and PPDR applications), is described herein. This casemay be typified by mobility that is typical for cellular applications,by access of all WTRUs, (i.e., discoverable WTRUs and seeking WTRUs),and to infrastructure, (base station or relay station (RS)), nodes thatmay operate at a data rate that is sufficient for controlling signalingbetween them. Unlike the PPDR case, network access and setup precededata communication, and access latency requirements may not be as strictas for PPDR, (but stricter than for the M2M case). The WTRU-WTRU nodediscovery may be either event triggered or scheduled periodically bytaking advantage of the central infrastructure node.

In one scenario, WTRU-WTRU direct communications, (e.g., peer-to-peerdirect communications where the two WTRUs are the source and sink of thedata), may be used for both PPDR and commercial applications, (e.g.direct video streaming). In another scenario, peer relaying at a datarate that is substantially higher than what is directly available from abase station may be used.

One of the constraints for network synchronization in an orthogonalfrequency division multiplex (OFDM) communications system is that theOFDM system relies on time and frequency synchronized reception ofwaveforms from various transmitters in order for them to be separated.All available uplink (UL) signals in IEEE 802.16m may be received at thebase station within the extended OFDM symbol (including cyclic prefix(CP)). For normal transmissions from the WTRU to the base station, thismay not be an issue, as the WTRU may be synchronized at least in thedownlink (DL) prior to any transmission. A device that does not have anaccess to the reference signal may not be synchronized in time orfrequency. Signaling to the network may require trying many differenttimes and possibly frequency offsets, in conjunction with power ramping.The process may cause a substantial delay and create a lot ofinterference, depending upon the type of signal used, (e.g., the delayand interference may be particularly severe for OFDM signals).

For M2M applications, as network discovery occurs rarely and does notneed to be updated very often, the full functionality that is typicallybuilt into a relay in order to simplify access to it by a WTRU, (e.g.,preamble, control channels, broadcast of full network information, andthe like), may not be built into the WTRU. Doing so may unnecessarilydrain battery powers and create a large amount of interference to otherbase stations. (This situation is not very different from Femto basestation, except that the number of mobiles may far exceed the number ofFemto base stations). In accordance with one example, associated devicesmay transmit little or no signals for that purpose. Those transmissionsmay be coordinated with the device sleep cycles.

In accordance with one example, a discoverable WTRU in an associatedstate may transmit using few resources at a low power. Unlike in anormal access, in the node discovery, the discoverable WTRU transmitsand the seeking WTRU receives little or no information regarding theaccess parameters. The challenge is therefore to design a process bywhich such parameters are learned during the discovery and associationprocedure, and not broadcast, and yet provides a flexible access. In oneexample, interference created by signals transmitted by the discoverableWTRU is minimized by a group of WTRUs transmitting the same accessinformation using the same resources at a low power level. Thus, agroup-based preliminary access stage is followed by WTRU-specificaccess.

For WTRU-WTRU direct communications in the absence of infrastructure, asfew steps as possible may be performed for quick and robust networkaccess. Considering the (relatively) small number of devices and relaxedbattery considerations (relative to M2M communications), regularlytransmitted information may be more excessive without major impact oneither interference or battery life. PPDR applications may supportunicast (peer to peer) as well as multicast (peer to multiple peers)applications.

For WTRU-WTRU direct communications under control of a base station, itis assumed that both the seeking WTRU and the discoverable WTRU areattached to a base station, and therefore already roughly synchronizedwith each other, and the base station already knows of their existenceand needs. The base station then needs to know the path loss, (i.e.,quality of a radio link), between the seeking WTRU and the discoverableWTRU.

FIG. 2 shows a network 200 including a seeking WTRU 205 and adiscoverable WTRU 210 configured to perform an access initializationprocedure. The seeking WTRU 205 may include a receiver 215, a processor220 and a transmitter 225.

The discoverable WTRU 210 may include a receiver 230, a processor 235and a transmitter 240. The receiver 230 may be configured to receive acommand signal from a base station (not shown) instructing thediscoverable WTRU 210 to transmit a timing signal 245. The processor 235may be configured to control the transmitter to 240 transmit the timingsignal 245 in accordance with the command signal. The timing signal mayinclude at least one of a primary preamble or a secondary preamble.

The receiver 215 in the seeking WTRU 205 may be configured to receivethe timing signal 245 from the discoverable WTRU 210 and, in response,the processor 220 may be configured to control the transmitter 225 totransmit an HSS 250 to the discoverable WTRU 210. The receiver 230 inthe discoverable WTRU 210 may be further configured to receive the HSS250.

This procedure may apply, but is not limited to, M2M applications. Itmay be assumed that the discoverable WTRU 210 is already attached to abase station, but the seeking WTRU 205 is not. Initially, the seekingWTRU 205 may not have any information on the existence, timing, orparameters of any network in the area. The discoverable WTRU 210 mayprovide timing information to the seeking WTRU by transmitting (e.g.,periodically) a timing signal (TS) 245. The TS 245 may be insensitive tothe receiver timing. Thus, some waveforms may be received without anytiming information but such information may still be determined. Forexample, any sequence that repeats itself in the time domain may bedetected by continuously auto-correlating a time window against its lag.A primary advanced preamble (PA-preamble) may be used as the TS 245,which may provide at least one of its own timing information and systembandwidth information. If additional information needs to be provided(for example group membership), the TS 245 may include a PA-preamble anda secondary advanced preamble (SA-preamble), whereby the SA-preamble ismapped to the group. The PA-Preamble may convey system bandwidth bysequence. The SA-preamble may convey a cell-ID or a WTRU-ID.

The discoverable WTRU 210 may transition between an idle mode/state or aconnected mode/state, and it may be assigned a sleep pattern that makesit unavailable at certain predetermined time periods. When thediscoverable WTRU 210 is in an idle mode/state, it may be preconfiguredto wake up in order to be able to be discovered by a potential seekingWTRU, such as seeking WTRU 205. The wakeup epochs may coincide withthose meant to receive paging. When the discoverable WTRU 210 is in aconnected mode/state, it may be in a sleep, (i.e., a discontinuousreception (DRX)), pattern. Thus, any such sleep pattern may besynchronized by the WTRU 210 such that its “awake” epochs are sufficientto be discovered and, if it is a part of a group, the WTRUs of the groupmay be synchronized to wake at same time. The timing and length ofwakeup periods for discovery may be independent of any other sleeppattern configured for other purposes.

Multiple discoverable WTRUs 210 may transmit the same TS 245 at the sametime on the same resources. A receiver may interpret such a waveform asa single transmission with a multi-path. Due to the short propagationtime, this may not be an issue. The advantage of multiple discoverableWTRUs 210 transmitting the same signal, (i.e., TS 245), is that thesignals received from multiple sources are summed constructively ratherthan interfering with each other. As a result, the transmission powermay be reduced.

There may be two scenarios for the timing of the TS 245. In onescenario, discoverable WTRUs in a peer group may transmit the samewaveform at the same time. In an alternate scenario, different peergroups may transmit a different TS 245, either at the same time or atdifferent times. The benefit of transmitting the same waveform may bethe reduction of the transmission power of the TS 245. Alternatively, oradditionally, each discoverable WTRU 210 may transmit the TS 245 atdifferent times. This may be beneficial when there is a large number ofpotential discoverable WTRUs 210, by reducing the average discoverytime.

The transmission epoch may be periodic or randomized. In the lattercase, the discoverable WTRU 210 may determine its own transmissionepochs. For example, these may be determined when the discoverable WTRU210 is in a DRX or sleep states. For both variants, the discoverableWTRU 210 may not receive, (e.g., a base station preamble), and transmit,(e.g., a TS 245), at the same time.

A base station (not shown) in the network 200 of FIG. 2 may instruct thediscoverable WTRU 210 which TS to transmit, when to transmit it, at whatpower level to transmit it, and/or which sub-carriers may carry the TSsequence. The periodicity of such transmissions, (i.e., the distributionof time intervals between transmissions), may affect the network entrytime and/or battery consumption of the discoverable WTRU 210. When thediscoverable WTRU 210 is attached to a network indirectly, theinstruction may be relayed, (through relays or through other WTRUs).

The length and frequency of transmission of the TS 245, (whetherperiodic or not), may play a major impact on WTRU-WTRU discovery successrate, its latency, tolerance to WTRU mobility, interference overhead andbattery consumption. Since the seeking WTRU 205 is not associated withthe network, it may be neither synchronized with the network nor withthe discoverable WTRU 210. As a result, it may not be possible for theseeking WTRU 205 to align the time line properly to receive the TS 245in accordance with the TS transmission schedule. In order to receive theTS 245, the seeking WTRU 205 may attempt to continuously receive eachsymbol at least over one predefined longest TS transmission period, (thesub-carrier configuration of the TS 245 may also be predefined and thusknown to the seeking WTRU 210). The seeking WTRU 205 may attempt toreceive the TS 245 according to an arbitrary predetermined schedulethat, combined with the predetermined TS transmission schedule, maygenerate a satisfactory probability of that seeking WTRU 205 receptioncoinciding with the discoverable WTRU 210 transmission in time domain.This may be possible because, as with randomized TS epochs, theprobability of reception may depend on the cumulative open window time,and not its exact timing.

If the seeking WTRU 205 does not receive the TS 245, it may wait and tryagain. The wait time, number of attempts and failure criteria may beconfigured at the seeking WTRU 205 as desired. Upon receiving the TS245, the seeking WTRU 205 may acquire the following information: networktiming, (the IEEE 802.16m PA-preamble provides symbol, frame andsub-frame timing), system bandwidth (depending on the TS 245, true foruse of the IEEE 802.16m PA-preamble), the cell identity and type thediscoverable WTRU 210 is associated with, (if using the IEEE 802.16PA/SA-preamble), path loss (i.e., link quality) information, (if the TS245 transmit power level is fixed and predefined), peer group identityfor the seeking WTRU 205 to determine whether a response is warranted,(if peer group information is embedded in the TS 245 sequence), or thelike.

At this point, the network 200 or the discoverable WTRU 210 does notknow the existence of the seeking WTRU 205. Therefore, as shown in FIG.2, the seeking WTRU 205 may transmit a handshake seeking signal (HSS)250 indicating, as a minimum, its presence. The discoverable WTRU 210may monitor for such an HSS 250 after sending the TS 245. Listeningresources may be predefined and the mapping may be known to the seekingWTRU 205, or determined from signals received by the seeking WTRU 205from the discoverable WTRU 210, (e.g., the type of TS). The nature ofthe listening resources depends on the information and waveform used bythe seeking WTRU 205. In accordance with one example, the waveform maybe a simple time domain waveform. In this case, the listening resourcesmay be a listening window or windows at predetermined times relative tothe TS 245 and/or the sub-carriers applied for the seeking WTRU 205transmission. In the absence of a seeking WTRU 205, the addedinterference in the network 200 may be an infrequent transmission of avery short waveform, followed by several (similarly short) listeningwindows. Thus, the interference created by the signals (TS 245) forassisting the neighbor discovery process may be minimal.

The seeking WTRU 205 may transmit a waveform, (e.g., HSS 250 in FIG. 2),to make itself known to the discoverable WTRU 210 and/or the network200, (also referred to as “initial handshake”). In order to minimize theinterference, the seeking WTRU 205 may transmit the HSS 250 once, orstart transmission of the HSS 250 at a low power and ramp up thetransmission power during the listening windows, until a response isreceived or an allowed maximum power is reached, in which case rampinghas failed. Ramping may be used by the discoverable WTRU 210 forestimating path loss, (i.e., the quality of a radio link establishedbetween the seeking WTRU 205 and the discoverable WTRU 210). Even if notnecessary for path loss estimation, ramping may have benefits inreducing unnecessary interference.

The seeking WTRU 205 may determine which discoverable WTRUs 210 torespond to. The seeking WTRU 205 may send an HSS 250 in response to a TS245 from an allowed peer group. In this case, the mapping of the peergroup to signals sent from the base station, (e.g., TS 245), may beknown in advance, (e.g., hard coded). The initial power level, apreamble interval, and the power ramping steps may be predetermined.With the listening windows, the discoverable WTRU 210 may know how manyramping steps have occurred.

The discoverable WTRU 210 may estimate, for example, the path loss,(i.e., radio link quality), between the discoverable WTRU 210 and theseeking WTRU 205, and may report the estimate to a base station (notshown) in the network 200. To ensure that an appropriate threshold isused, the base station may instruct the discoverable WTRU 210 to reportall received signals, or statistics, (such as average and spread),derived from such signals, whether they exceed the threshold or not,such that the threshold may be adjusted if necessary. With the knowledgeof the ramp-up step size and the initial power, the discoverable WTRU210 may determine the transmission power and may estimate the path loss.Alternatively, no ramping may be performed and the HSS 250 power may befixed and known. For example, the power level of the HSS 250 may be thesame as the TS 245 power level. HSS resources may be given in terms ofthe TS 245, (e.g., using fixed resources every n-th frame starting agiven time after the TS 245).

Examples of an HSS in IEEE 802.16m may be a PA-preamble (same as the TS245), the IEEE 802.16m ranging preambles (either for synchronized ornon-synchronized devices), and/or an IEEE 802.16m sounding signal. Sincethe seeking WTRU 205 may now be roughly synchronized with thediscoverable WTRU 210, the HSS 250 may not need to beself-synchronizing. The resources for the sounding as HSS 250 may beimplicitly allocated by a base station through the allocation of TStransmission epochs. The base station may clear those times fromsounding by other devices. For example, for TDD, the first OFDMA symbolin the second UL sub-frame in the frame which contained the TS 245 maybe reserved for the HSS 250. If ramping is used, then subsequent epochsmay be assigned. The identity (ID) or timing of the HSS 250 may bedetermined based on the TS 245 that was received. Specifically, if agroup ID is used for the TS 245, then same group ID may be used. If theTS of different peer groups transmit at different times or sub-carriers,then the HSS 250 may carry the group information implicitly. This allowsthe HSS 250 to carry the path loss information as measured at theseeking WTRU 205. For example, if the IEEE 802.16m PA-preamble and/orSA-preamble are used for the HSS 250, then the SA-preamble may be mappedto the received signal level.

Not necessarily all discoverable WTRUs 210 that have received the HSS250 need to respond. A determination of who responds may be based onrelevant information, (e.g., estimated path loss), and may be made in adistributed manner or under direct base station control. Specifically,the seeking WTRU-discoverable WTRU 205/210 path loss estimate may beobtained as explained above, and a seeking WTRU-base station path lossestimate, obtained in the usual manner, may be used to determine thebest discoverable WTRU 210. In a centralized control mode, discoverableWTRUs 210 which have received the HSS 250 may send that information tothe base station, and the base station may decide which should respondbased on the information, (e.g., path loss estimate and other parameterssuch as capabilities of the forwarding WTRU, its battery level, and/orits own traffic load). To reduce the signaling load between thediscoverable WTRU 210 and the base station, it is possible to limit thatsignal to discoverable WTRUs 210 that obtain a low enough path lossestimate.

The centralized control mode may introduce a latency in responding tothe ramping and, as a result, may cause extra battery consumption by theseeking WTRU 205, and possibly a failed hand-shaking effort, because thediscoverable WTRU 210 may not respond to the ramping upon receiving it,and may send the information to the central node and await instructionsin return. During this round-trip delay, the HSS 250 ramping may stillbe on-going.

Alternatively, the responding discoverable WTRU 210 may be controlled ina distributed manner by predetermining a threshold based on at least oneradio link quality (e.g., path loss) value. The threshold may besignaled by the base station, hard wired or unspecified. Traffic loadmay be taken into account in a similar manner, (e.g., by a threshold onbuffer occupancy). Note that the distributed procedure doesn't guaranteethat at least one discoverable WTRU 210 may respond. Any discoverableWTRU 210 that receives the TS 245 may send that information to the basestation. The base station may adjust the response parameters and signalit to the discoverable WTRU 210, and/or the seeking WTRU 205 may tryagain after some predetermined time period elapses. The transmissionpower for the discoverable WTRU 210 at this stage may be determined fromthe radio link quality estimate.

The network 200 in FIG. 2 may support the transmission of broadcastinformation by the discoverable WTRU 210. The benefit may be inpreventing the constant broadcast of full access information when, mostof the time, access information is not required. Instead, reducedtransmission, (e.g., limited to a synchronization signal), may betransmitted. The transmission of the TS 245 and HSS 250 may serve as afirst phase in causing suitable discoverable WTRUs 210 to transmitdiscoverable WTRU-specific and sufficient access information thatfulfills the same functions as base station timing and broadcastsignals.

Given the short range to forwarding WTRU and low mobility, it may beassumed that the first phase, (i.e., the exchange of the TS 245 and theHSS 250 between two WTRUs), may achieve sufficient synchronization, andadditional synchronization steps may not be necessary. However, ifadditional synchronization steps are necessary, they may be carried outin a normal manner.

FIGS. 3A and 3B are flow diagrams of additional procedures 300 and 350,which may include the steps described above, to complete the access tothe discoverable WTRU.

In the procedure 300 of FIG. 3A, after completing the first phase, thediscoverable WTRU 210 may transmit an identification signal 305 thatincludes a WTRU identity (ID) (i.e., a preamble) that may be temporary(i.e., meaningful within a cell). Given that bandwidth and timinginformation are already available, there may not be any need to transmita PA-preamble. Instead, an SA-preamble may uniquely identify thediscoverable WTRU 210. The short duration of this signal makes itsuitable to stop the power ramping of the HSS 250, but other signals mayalso be used for this purpose.

Once the HSS 250 is terminated in response to the successful receptionof the response 305 of the discoverable WTRU 210, the seeking WTRU 205may prepare to receive the broadcast information of the discoverableWTRU 210 at a predefined time instance and sub-carrier locations.Alternatively or additionally, the discoverable WTRU 210 may thentransmit sufficient access information, (e.g., system information (SI))that the seeking WTRU 205 may use to derive where to access thebroadcast information. The access from the seeking WTRU 205 may beperformed through the use of a common channel or a dedicated channel.The use of a dedicated channel may be suitable for low probability ofcollision of network access attempts, while the use of a common channelmay be suitable for higher collision probability. In both alternatives,the information may include the ID of the discoverable WTRU 210.

With the use of common channels as shown in the procedure 300 of FIG.3A, the discoverable WTRU 210 may transmit, for example, a WTRU-specificPA-preamble and SA-preamble (305), and/or a primary and secondarysuperframe header (SFH) (310) with sufficient content (i.e., minimalcontent) to allow access to the seeking WTRU 205. When receiving theSFH, the seeking WTRU 205 may know the common channel (“ranging”) accessparameters and may perform, for example, a ranging procedure via arandom access channel (RACH) (315), whereby a preamble is sent from aWTRU to a base station, is ramped up, and there is a response andbandwidth allocation by which the WTRU may send back some information.It may not be required that the preamble ID matches the TS 245, as longas the preamble ID is a “legitimate” ID.

Either a preamble 305 followed by an SFH 310 or its equivalent, (i.e.,any message that contains access information), or an SFH 310 without apreamble 305, may be transmitted. The first of those may be at a knownlocation relative to the HSS location and/or its type. The seeking WTRU205, having sent an HSS 250, may need to know where to look for theresponse. Thus, for example, the response may be sent a given number ofsub-frame or frames after the HSS 250. Additionally, the timing of theresponse may depend on the choice of sequence for the HSS 250, (e.g.,different sequences may lead to different delays between the HSS 250 andthe response). The SFH resources may be partially determinable from thepreamble 305. The SFH or its equivalent may have an embedded ID. If asecondary preamble is used that has an ID mapped to it, then it may usethe same ID as in the SFH.

There may be several ways to assign IDs. In one embodiment, the ID maybe a unique ID assigned to every WTRU. If this is the case, there may bemore IDs than may be supported by the preamble alone. The ID informationin the SFH 310 may be used instead. Alternatively, the ID may beconcatenated with the ID implied by the preamble (if used).

In another embodiment, the ID may be randomly chosen by the discoverableWTRU 210. It is possible that two or more discoverable WTRUs 210 maychoose the same ID. If that happens and the resources for ranging arethe same, then the seeking WTRU 205 may effectively send ranging to bothof the discoverable WTRUs, which may create a collision when theyrespond. To resolve it, each discoverable WTRU 210 may include itsrandom ID, plus a second random ID to be concatenated with it. Then, theseeking WTRU 205 may not decode the response and may ramp up and resendits HSS 250, or the seeking WTRU 205 may decode one response and includethe concatenated ID in a further transaction. The discoverable WTRU 210with that ID may continue to respond.

With the use of dedicated channels as shown in the procedure 350 of FIG.3B, the SFH transmission may be skipped and a resource allocation 365including specific UL resources may be signaled directly to the seekingWTRU 205. Other parameters, (e.g., multiple-input multiple-output (MIMO)mode), may also be signaled. The access information may be transmittedon an SFH-like waveform. The resources for its transmission may bepredetermined.

To resolve conflicts, the seeking WTRU 205 may access a discoverableWTRU 210 that has sent a response 370 that may include the ID of theseeking WTRU 205 and the discoverable WTRU 210. The discoverable WTRU210 may acknowledge the response 370 by sending the ID of the seekingWTRU 205 (375). Other data may be added.

To prevent downlink interference between the SFH or A-MAP (i.e.,mapping) transmission of two or more discoverable WTRUs 210,transmission time of the SFH or A-MAP may be chosen randomly followingthe SA-preamble. The resources used for SFH or resource allocation maybe determined from the preamble or may be predetermined.

If no response to the HSS has been received after a given number oframping steps, (or alternatively at maximum power), the seeking WTRU maystop the access procedure and try again after some random back-off time.If no response is received, depending on the type of channel used, theseeking WTRU may re-start the transmission of the HSS after some randomback-off time, or may try ranging again after some random back-off timein the normal manner.

In another embodiment, the TS may carry a group ID of a plurality ofdiscoverable WTRUs that is potentially different from a cell ID. Thismay be particularly useful where there are many groups, and discoverytime is to be kept short.

FIG. 4 shows an example placement of a TS 400 transmitted by adiscoverable WTRU in an IEEE 802.16m superframe 405. A base stationtransmits a TS 410. The TS 400 sent by the discoverable WTRU may includean SA-preamble 415 and a PA-preamble 420. In this example, the TS sentby the base station may include an SA-preamble 425 and a PA-preamble430, which coincide with the preambles 415 and 420 of the TS 400 sent bythe discoverable WTRU.

The TS 400 may be transmitted in a downlink (DL) access zone wherediscoverable WTRUs are set to transmit while the seeking WTRU isreceiving. However, no additional transmit/receive (i.e., switching)gaps are necessary due to the TS 400.

The TS 400 may not have to be transmitted every superframe. To depictits placement, a superframe may be denoted without a TS as “0”,super-frames that contain a TS of group “A” as “A”, and superframes thatcontain a TS of group B as “B”. Thus, as an example, a periodic, singlegroup may be depicted by A0000000A0000000A0000000A . . . ; a periodic, 2groups may be depicted as A0B00000A0B00000A0B00000A . . . ; and arandomized, single group may be depicted as A00A0000000000000AA000000A .. .

FIG. 5 shows an example of transmission opportunities for sounding asHSS in a TDD frame. An HSS may use a sounding signal. HSS timing andcode combination may correspond uniquely to a TS code that, in itself,corresponds to a discoverable WTRUs group ID. The HSS may be sent duringnormal sounding transmission epochs of the access zone, (i.e., firstOFDMA symbols of the sub-frames of the access zone). HSS may betransmitted in the UL access zone, therefore no additionaltransmit/receive gaps may be necessary. Path loss information may not beencoded into the HSS.

FIG. 6 shows an example of a plurality of superframes used by a basestation, two discoverable WTRUs and two seeking WTRUs. The superframesmay include HSSs 605, SA-preambles 610, PA-preambles 615, SFHs 620 andTSs 625. In this example, a discoverable WTRU 1 and a discoverable WTRU2 may not initially transmit an SFH, as they may not support anyattached devices. However, the discoverable WTRU 1 and the discoverableWTRU 2 may transmit a TS with different codes. Upon satisfying group andpotentially path loss requirements, a seeking WTRU 1 and a seeking WTRU2 may respond with the ramping up of an HSS (of different codes). Whenthe HSS is received, the discoverable WTRU 1 and the discoverable WTRU 2may respond by transmitting an SFH and both SA-preamble instances. TheSFH may be protected by a cyclic redundancy check (CRC). Therefore, alegitimate SFH may be easy to identify from other data. At this point,discoverable WTRU operation may be identical to relay signaling, and theseeking WTRU may perform network entry as usual.

The discoverable WTRUs that are not associated with any seeking WTRUsmay not create any interference to the base station SFH, nor do theyconsume battery power to transmit it. (In IEEE 802.16m, an SFH mayconsume 5 OFDMA symbols in each superframe, which may be consideredequivalent to discoverable WTRUs transmitting roughly 2.5% of the time).

In another example, a TS code may not carry any ID, (i.e., alldiscoverable WTRUs may be discovered by all seeking WTRUs). Thisprocedure may be useful when seeking WTRUs are few, and attachments arefar between, so it is important to minimize TS energy and interference.As previously described, a TS may include a PA-preamble. Itstransmission, when not in a sleep mode, may coincide with the basestation PA-preamble. The PA-preamble code may identify it as adiscoverable WTRU, (rather than a base station).

A seeking WTRU may respond with an HSS, (possibly if path loss criteriaare met). Several seeking WTRUs may respond at the same time using thesame sounding code. The HSS may carry the seeking WTRU group or deviceID. Upon reception of the HSS, (ID and path loss criteria are met), thediscoverable WTRUs may start to transmit an SA-Preamble and SFH. SeekingWTRUs may start network entry procedures.

In another embodiment, both discoverable and seeking WTRUs may be underthe control of a base station. This may be most suitable (but notlimited to) throughput enhancements in high data rate applications,e.g., streaming videos. This embodiment may be applicable topeer-to-peer data communication and/or peer relaying for high data rate.

There are several alternatives for this case which may depend on theinformation the network may have prior to initiation of the discovery.The information may relate to the specificity of the subject of thediscovery and with path loss. The WTRUs may not know in advance whichother WTRUs they want to be connected to. This may be useful inpeer-to-peer data communications in the context of social networking orother applications where the peer-to-peer communication takes placebetween peers that happen to be in the area. It may also be useful whenattempting to discover any peer relay which happens to be in the area.In this scenario, a seeking WTRU may want to find discoverable WTRUsthat are within sufficiently short range for peer-to-peer communication.Alternatively or additionally, two WTRUs may seek each other, e.g., toaugment the data rate they may support through the base station.

In any scenario, it may be helpful if the base station has informationregarding the physical location of the WTRUs. Such information may beobtained by GPS, by beamforming performed at the base station, by timingadvance correction, by location measured at the WTRU, (e.g., timedifference of arrival (TDOA)), or any combination thereof. It may beassumed that physical proximity as determined from such locationinformation may predict peer-to-peer path loss. (This is clearly not thecase, for example, for two WTRUs that are located on different floors inthe same building). If both assumptions are assumed to be met, then itmay be useful for the base station to construct a proximity map forWTRUs in its area that predicts the economy of the connection (inresources, latency, and the like) relative to communication through thebase station. It may be up to the base station to keep its locationinformation updated. Thus, for example, if WTRUs in idle state are toremain discoverable, then they may be scheduled to update their locationinformation as necessary.

If a prior path loss estimate exists, the base station may instruct thediscoverable WTRUs to transmit a signal that may be detected by seekingWTRUs in the cell. The seeking WTRUs may include one or more WTRUs in aparticular proximity group. They may be notified of the discoveryattempt and necessary configuration of the discovery process. Even ifproximity information isn't available, the procedure has a built-in pathloss measurement that may be used by the network to assign de-factoproximity.

A reference signal that may be similar to a TS may be used to enableother WTRUs to measure path loss between them. Transmission power may beindicated by the network or base station. For example, the base stationmay instruct a WTRU to raise its power if other WTRUs in the area havefailed to receive it. Alternatively or additionally, the transmissionpower may be predefined. Either effectively defines the discovery rangeand enables the path loss derivation once the TS transmission isdetected and received. The latter may reduce the overhead in connectionwith the discovery process.

In a variant of this procedure, TS power may be stepped (ramped) up inpredetermined steps such that the transmission power at any given timeis known and may be used for a path loss (PL) estimate. Transmissiontime and/or frequency may be indicated by the network or base stationand provided to the WTRUs that need to receive it. Groups of users maybe separated in time and/or frequency or code. Also, the frequencyresource may be predefined to reduce overhead.

For this procedure, it may be assumed that both discoverable WTRUs andseeking WTRUs are in a connected mode at the time of discovery and notin a sleep mode. It may be the base station's responsibility to makesure that the sleep patterns (if any) of the WTRUs are matched. User orgroup identity may be encoded similar to encoding of user group ID.Recipient WTRUs may be notified of transmission time and frequency ofgroup or groups they are to detect, as well as transmission power.

A WTRU that receives a timing signal may report to the base station. Thereporting itself may be dependent on reception level or path loss (radiolink quality) and/or reception of TS from a certain group. For example,received signals with a low power level or signals with a high path lossmay not be reported to the base station. A threshold used fordetermining whether or not to report signals to the base station may beprovided by the base station. Other thresholds, such as battery status,radio link quality with the base station, or the like, may also be usedto avoid unnecessarily reporting to the base station. The reportedinformation may include reception level or path loss (i.e., radio linkquality), WTRU and/or group ID and time/frequency of the TS, and thelike. To ensure that an appropriate threshold is used, the base stationmay instruct the WTRU to report all received signals, or statistics,(such as average and spread), derived from such signals, whether theyexceed the threshold or not, such that the threshold may be adjusted ifnecessary.

FIG. 7 shows an example procedure 700 implemented when a seeking WTRU705 and a discoverable WTRU 710 are under the control of a base station715. When the discovery is coordinated by the base station 715, one TSattempt may be enough because the seeking WTRU 705 may be informedwhether the discoverable WTRU 710 is transmitting and both aresynchronized.

In 720, a neighbor discovery setup procedure may be implemented by thebase station 715 with the discoverable WTRU 710. In 725, a neighbordiscovery setup procedure may be implemented by the base station 715with the seeking WTRU 705. This may be implemented in unicast signalingfrom the base station 715 to a respective discoverable WTRU 710, oralternatively different groups of discoverable WTRUs 710 may beinstructed by the base station 715 to take on different roles. In 730,the discoverable WTRU 710 may send a TS 730 to the seeking WTRU 705. In735, the seeking WTRU 705 may send path loss (i.e., radio link quality)measurement information it has measured between the seeking WTRU 705 andthe discoverable WTRU 710, and other information, such as the receivedcode of the TS 730, and its timing relative to the base station 715.

Peer-to-peer communications with one out-of-coverage WTRU is describedherein. While some protocols may need to change to accommodate thiscase, specific procedure for WTRU discovery may not be required. It maybe necessary to separate the TS waveforms from the normal base stationpreambles. For example, this may be implemented by transmitting the TSin a frame that is not used by the base station.

If grouping is required at this point, then the TS may be composed of aPA-preamble and a SA-Preamble as shown in FIG. 4. Otherwise, theSA-preamble may be omitted. The power level may be signaled to bothdiscoverable and seeking WTRUs. A seeking WTRU may check the grouping,compute path loss and create a report if particular criteria are met.

An access procedure when no infrastructure nodes are available isexplained herein. This procedure is suitable for (but not limited to)PPDR mobile applications in cases where infrastructure nodes cannot bereceived by any WTRUs in an area. This procedure may be adapted toachieve the low access latency and the high rate of network entry.

An important consideration is the speed of creating a connection, (dueto the fact that connections are created just prior to sending of data).A peer group for this scenario may be defined as the group ofsubscribers that may form sub-networks.

This procedure may maintain as many subscribers synchronized as desired,because even though communications in this scenario occurs insub-networks, synchronizing sub-networks that exist in the same carrierand geographical area reduces interference in general and allows formore sophisticated interference management or reduction procedures, andsynchronized devices may require shorter connection setup time.

The requirements for rapidly establishing a connection does not allowfor many steps for the access. One of the means to shorten the requiredtime to establish the connection is to avoid random access as much aspossible. The procedure may use WTRU IDs.

In order to shorten connect time, devices on the network (whetherconnected or not) may be (receiver) synchronized and may transmit a timesynchronization signal (e.g., TS). Subscribers in a peer group maytransmit the same waveform at the same time. Different peer groups maytransmit a different TS, either at the same or different times. APA-preamble and SA-preamble may be used if grouping information is to beconveyed. Network entry parameters that are related to the SFH may besignaled by adding an SFH.

In accordance with one embodiment, WTRUs in the network that receivedthe TS may modify it to a different TS (i.e., TS′) and relay it at adifferent time. TS′ may be mappable from the TS. The time difference maybe known in advance. Relaying may be on a peer group basis and thegroups may be predetermined.

The pair TS-TS′ relationship is such that receiving one of them providessufficient timing information and they may share the same ID. There aremany ways by which the properties above may be achieved. One example isthat TS′ uses similar codes to TS and that the mapping of codes betweenTS and TS′ is known.

In accordance with another example, a single type of TS may be used. AWTRU may alternate between receiving the TS and transmitting it. Inorder to regulate the transmitting and receiving, the decision may beleft to the WTRU under the condition that synchronization (in time andfrequency) may be maintained and that a certain fraction of the TS maybe transmitted. Alternatively, the receive/transmit pattern may bepredetermined.

A WTRU that needs to adjust its timing by a significant factor afterreception of the TS may avoid transmitting it. This may effectivelyremove fast moving WTRUs from a relaying group and improve the overallnetwork synchronization quality. As a result, WTRUs may be synchronized.If an SFH is used, then a network entry may follow that of a WTRU to abase station. A seeking WTRU that detects a discoverable WTRU that itwants to connect to may perform an unsynchronized ranging network entryto that discoverable WTRU. If an SFH is not used, then a simplifiednetwork access may take place.

Seeking WTRUs may attempt to indicate which discoverable WTRU(s) it mayform a connection to. A seeking WTRU may start by sending a connectionestablishment signal (CES) to one or more discoverable WTRUs. The CESmay include a sequence that indicates the seeking WTRU ID, such as anIEEE 802.16m SA-preamble, and an OFDM signal sent at knowntime/frequency resources. Those may be determined by the seeking WTRUID. Alternatively, the OFDM signal may be transmitted on resourcesrandomly selected out of a group of resources. At least one of thefollowing information may also be included: seeking WTRU ID (may benecessary for random resources case), DL resources to be used formulticast (common) data, a list of discoverable WTRU IDs for each DLresources for individual part, UL resources for feedback (includingbandwidth request), and UL resources for data (persistent allocation),or a transmit power used and estimate of received interference at theseeking WTRU. Instead of a single seeking WTRU ID, the message mayinclude a group ID. In this case, UL resources may be provided forfeedback and bandwidth request (BR).

Transmission power may be set high enough for a reasonable success rate.A discoverable WTRU that detects its ID responds via indicatedresources. The initial transmit power may be determined by usingparameters (transmit power, interference and own measured receivedsignal level, and the like).

If the seeking WTRU does not receive a response from any indicateddiscoverable WTRUs, it may raise power and repeat the process, but maynot need to repeat all recipients IDs.

Discoverable WTRUs and seeking WTRUs in this case may be determined byneed, not by topology. WTRUs therefore may be discoverable if theytransmit the necessary signals. However, two WTRUs may end up attemptingto perform network entry into each other at the same time. This may beavoided by establishing a random wait time between the TS and the entryattempt.

IEEE 802.16m defines several UL and DL channels to be used for differentpurposes. These may be categorized by their physical characteristics andby their access mode (scheduled or contentious). Data channels may beused to transmit user data and medium access control (MAC) controlmessages. Data channels may be scheduled (persistently or per request),and contain user-specific quadrature amplitude modulation (QAM) data onpredefined time/frequency (T/F) resources. Reference signals (pilot) maybe embedded in other channels. Data and reference channels may not beconsidered useful for node discovery due to unavailable location orother information and the resulting difficulties in detection and highoverhead to the node to be discovered. UL feedback channels may carryspecific, predefined feedback information, which entail high overhead.

Ranging preambles (RPs) for non-synchronized WTRUs are designated bysub-frame and sub-band. Sub-bands may be determined by cell ID. Rangingpreambles may be constructed off a Zadoff-Chu sequence with cyclicshifts. There may be up to 32 initial RP codes. Reception of thiswaveform assumes that it arrives within the OFDM symbol time (includingcyclic prefix). For normal ranging, this may not be a problem as a WTRUmay already be synchronized in DL prior to the sending of a rangingpreamble.

Sounding channels may be allocated a single OFDM symbol, up to one persub-frame and are constructed off a predefined Golay sequence. A WTRUmay be instructed as to how to transmit a sounding signal. Sub-carriersare divided into sounding sub-bands, each 72 sub-carriers (for fastFourier transform (FFT) of 512, 1025 and 2048) and up to 25 sub-bands. AWTRU may be instructed to transmit on any combination of thesesub-bands, a maximum of 1728 sub-carriers.

Multiple WTRUs (or multiple antennas) may be multiplexed on the samesub-bands through frequency decimation or cyclic shift separation, inaddition to time separation by assigning to different sub-frame. Incyclic shift separation, different offsets of the Golay sequence may bechosen. Thus, WTRUs may be separated by the autocorrelation property ofthe Golay sequence. In frequency decimation, different sub-carriers maybe used for different WTRUs. Reception of this waveform may assume thatit arrives within the OFDM symbol time (including cyclic prefix). Fornormal ranging, this is not a problem as a WTRU may already besynchronized in UL prior to sending of ranging preamble.

A DL preamble may include a primary advanced and secondary advancedpreamble (PA-Preamble and SA-Preamble). The PA-Preamble occupiesalternating sub-carrier in a single OFDM symbol and therefore may have arepetitive (2×) structure in the time domain which may be blindlydetected with an autocorrelation detector and provide a timingreference. PA-Preamble may carry the information of system bandwidth.There may be a total of 11 distinct sequences, out of which 7 arecurrently “reserved.”

The SA-preamble may be bandwidth dependent. A choice of sequence mayindicate base station type (macro, Femto, relay, and the like) and cellID. This may be accomplished by selection of order of sub sequences,sequences themselves are quadrature phase shift keying (QPSK) modulated.In case of multiple antennas, different subsequences may be sent throughdifferent antennas. SA-preamble reception may require timing informationobtained from the PA-preamble.

FIG. 8 is a block diagram of an example base station 715 used to performthe procedure 700 of FIG. 7. The base station may include a receiver805, a processor 810 and a transmitter 815.

The base station 715 may implement node discovery for peer-to-peercommunication. The transmitter 815 may be configured to transmit acommand signal instructing a discoverable WTRU to transmit a timingsignal. The receiver 805 may be configured to receive a signal from aseeking WTRU that received the timing signal from the discoverable WTRU.The timing signal may include at least one of a primary preamble or asecondary preamble.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element may be used alone or in combination with any of theother features and elements. In addition, the embodiments describedherein may be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals, (transmitted over wired or wireless connections), andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, a cache memory, a semiconductormemory device, a magnetic media, (e.g., an internal hard disc or aremovable disc), a magneto-optical media, and an optical media such as acompact disc (CD) or a digital versatile disc (DVD). A processor inassociation with software may be used to implement a radio frequencytransceiver for use in a WTRU, UE, terminal, base station, Node-B, eNB,HNB, HeNB, AP, RNC, wireless router or any host computer.

The invention claimed is:
 1. A method of establishing peer-to-peercommunication, the method comprising: receiving, at a first wirelesstransmit/receive unit (WTRU), a command signal including an indicationof a timing signal to transmit, a transmit power level of the timingsignal, and a time to transmit the timing signal; transmitting, from thefirst WTRU, the timing signal in response to receiving the commandsignal; and receiving, at the first WTRU, a handshake seeking signalfrom a second WTRU in response to the timing signal.
 2. The method ofclaim 1 wherein the first WTRU belongs to a group of WTRUs controlled bya base station that transmitted the command signal.
 3. The method ofclaim 2 further comprising: the second WTRU estimating quality of aradio link established between the second WTRU and the first WTRU; andthe second WTRU determining whether or not to report the estimated linkquality to the base station.
 4. The method of claim 3 wherein thedetermination of whether or not to report the estimated radio linkquality to the base station is based on a threshold established by thebase station.
 5. The method of claim 1 further comprising: in responseto receiving the handshake seeking signal, the first WTRU transmittingat least one of a primary preamble, a secondary preamble, a primarysuperframe header (SFH) or a secondary SFH to the second WTRU; and thefirst and second WTRUs performing a ranging procedure.
 6. The method ofclaim 1 further comprising: the first WTRU ramping up the transmit powerlevel of the timing signal in predetermined steps; and the second WTRUestimating the quality of a radio link established between the secondWTRU and the first WTRU.
 7. A method of establishing peer-to-peercommunication, the method comprising: transmitting, at a first wirelesstransmit/receive unit (WTRU), a first signal; and receiving, at thefirst WTRU, a second signal having a transmission power that is rampedup during listening windows until a maximum allowed transmission poweris reached.
 8. The method of claim 7 wherein the second signal is ahandshake seeking signal that includes at least one of a primarypreamble or a secondary preamble.
 9. The method of claim 7 furthercomprising: in response to receiving the second signal, the first WTRUtransmitting at least one of a primary preamble, a secondary preamble, aprimary superframe header (SFH) or a secondary SFH to a second WTRU; andthe first and second WTRUs performing a ranging procedure.
 10. A methodof establishing peer-to-peer communication, the method comprising:transmitting, from a first wireless transmit/receive unit (WTRU), afirst signal to a second WTRU; and in response to receiving a secondsignal from the second WTRU, the first WTRU transmitting at least one ofa primary preamble, a secondary preamble, superframe header (SFH) or asecondary SFH, wherein the second signal is a handshake seeking signalthat has a transmission power that is ramped during listening windowsuntil a maximum allowed transmission power is reached.
 11. The method ofclaim 10 further comprising the first and second WTRUs performing aranging procedure.
 12. A wireless transmit/receive unit (WTRU)comprising: a receiver configured to receive a command signalinstructing the WTRU to transmit a timing signal, wherein the commandsignal includes an indication of the timing signal, a transmit powerlevel of the timing signal, and a time to transmit the timing signal;and a transmitter configured to transmit the timing signal in accordancewith the command signal, wherein the receiver is further configured toreceive a handshake seeking signal from another WTRU in response to thetiming signal.
 13. The WTRU of claim 12 wherein the transmitter isfurther configured to transmit at least one of a primary preamble, asecondary preamble, a primary superframe header (SFH) or a secondary SFHin response to the receiver receiving the handshake seeking signal.